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Bai-Lian Li

Publications and source records attributed to Bai-Lian Li.

14 recordsLinked to original sources
arXiv2021

Vegetation Impact on Atmospheric Moisture Transport under Increasing Land-Ocean Temperature Contrasts

Destabilization of the water cycle threatens human lives and livelihoods. Meanwhile our understanding of whether and how changes in vegetation cover could trigger abrupt transitions in moisture regimes remains incomplete. This challenge calls for better evidence as well as for the theoretical concepts to describe it. Here we briefly summarise the theoretical questions surrounding the role of vegetation cover in the dynamics of a moist atmosphere. We discuss the previously unrecognized sensitivity of local wind power to condensation rate as revealed by our analysis of the continuity equation for a gas mixture. Using the framework of condensation-induced atmospheric dynamics, we then show that with the temperature contrast between land and ocean increasing up to a critical threshold, ocean-to-land moisture transport reaches a tipping point where it can stop or even reverse. Land-ocean temperature contrasts are affected by both global and regional processes, in particular, by the surface fluxes of sensible and latent heat that are strongly influenced by vegetation. Our results clarify how a disturbance of natural vegetation cover, e.g., by deforestation, can disrupt large-scale atmospheric circulation and moisture transport. In view of the increasing pressure on natural ecosystems, successful strategies of mitigating climate change require taking into account the impact of vegetation on moist atmospheric dynamics. Our analysis provides a theoretical framework to assess this impact. The available data for Eurasia indicate that the observed climatological land-ocean temperature contrasts are close to the threshold. This can explain the increasing fluctuations in the continental water cycle including droughts and floods and signifies a yet greater potential importance for large-scale forest conservation.

physics.ao-ph↗
arXiv2020

Comments on "An evaluation of hurricane superintensity in axisymmetric numerical models" by Raphaël Rousseau-Rizzi and Kerry Emanuel

In a recent paper Rousseau-Rizzi and Emanuel (2019) presented a derivation of an upper limit on maximum hurricane velocity at the surface. This derivation was based on a consideration of an infinitely narrow (differential) Carnot cycle with the warmer isotherm at the point of the maximum wind velocity. Here we show that this derivation neglected a significant term describing the kinetic energy change in the outflow. Additionally, we highlight the importance of a proper accounting for the power needed to lift liquid water. Finally, we provide a revision to the formula for surface fluxes of heat and momentum showing that, if we accept the assumptions adopted by Rousseau-Rizzi and Emanuel (2019), the resulting velocity estimate does not depend on the flux of sensible heat.

physics.ao-ph↗
arXiv2019

Hurricane's maximum potential intensity and surface heat fluxes

Emanuel's concept of Maximum Potential Intensity (E-PI) relates the maximum velocity $V_{\rm max}$ of tropical storms, assumed to be in gradient wind balance, to environmental parameters. Several studies suggested that the unbalanced flow is responsible for E-PI sometimes significantly underpredicting $V_{\rm max}$. Additionally, two major modifications generated a considerable range of E-PI predictions: the dissipative heating and the power expended to lift water were respectively suggested to increase and reduce E-PI $V_{\rm max}$ by about 20%. Here we re-derive the E-PI concept separating its dynamic and thermodynamic assumptions and lifting the gradient wind balance limitation. Our analysis reveals that E-PI formulations for a balanced and a radially unbalanced flow are similar, while the systematic underestimate of $V_{\rm max}$ reflects instead an incompatibility between several E-PI assumptions. We discuss how these assumptions can be modified. We further show that irrespective of whether dissipative heating occurs or not, E-PI uniquely relates $V_{\rm max}$ to the latent heat flux (not to the total oceanic heat flux as originally proposed). We clarify that, in contrast to previous suggestions, lifting water has little impact on E-PI. We demonstrate that in E-PI the negative work of the pressure gradient in the upper atmosphere consumes all the kinetic energy generated in the boundary layer. This key dynamic constraint is independent of other E-PI assumptions and thus can apply to diverse circulation patterns. Finally, we show that the E-PI maximum kinetic energy per unit volume equals the local partial pressure of water vapor and discuss the implications of this finding for predicting $V_{\rm max}$.

physics.ao-ph↗
arXiv2017

Quantifying the global atmospheric power budget

The power of atmospheric circulation is a key measure of the Earth's climate system. The mismatch between predictions and observations under a warming climate calls for a reassessment of how atmospheric power $W$ is defined, estimated and constrained. Here we review published formulations for $W$ and show how they differ when applied to a moist atmosphere. Three factors, a non-zero source/sink in the continuity equation, the difference between velocities of gaseous air and condensate, and interaction between the gas and condensate modifying the equations of motion, affect the formulation of $W$. Starting from the thermodynamic definition of mechanical work, we derive an expression for $W$ from an explicit consideration of the equations of motion and continuity. Our analyses clarify how some past formulations are incomplete or invalid. Three caveats are identified. First, $W$ critically depends on the boundary condition for gaseous air velocity at the Earth's surface. Second, confusion between gaseous air velocity and mean velocity of air and condensate in the expression for $W$ results in gross errors despite the observed magnitudes of these velocities are very close. Third, $W$ expressed in terms of measurable atmospheric parameters, air pressure and velocity, is scale-specific; this must be taken into account when adding contributions to $W$ from different processes. We present a formulation of the atmospheric power budget, which distinguishes three components of $W$: the kinetic power associated with horizontal pressure gradients ($W_K$), the gravitational power of precipitation ($W_P$) and the condensate loading ($W_c$). We use MERRA and NCAR/NCEP re-analyses to evaluate the atmospheric power budget at different scales: $W_K$ increases with temporal resolution approaching our theoretical estimate for condensation-induced circulation when all convective motion is resolved.

physics.ao-ph↗
arXiv2017

The equations of motion for moist atmospheric air

How phase transitions affect the motion of moist atmospheric air remains controversial. In the early 2000s two distinct differential equations of motion were proposed. Besides their contrasting formulations for the acceleration of condensate, the equations differ concerning the presence/absence of a term equal to the rate of phase transitions multiplied by the difference in velocity between condensate and air. This term was interpreted in the literature as the "reactive motion" associated with condensation. The reasoning behind this "reactive motion" was that when water vapor condenses and droplets begin to fall the remaining gas must move upwards to conserve momentum. Here we show that the two contrasting formulations imply distinct assumptions about how gaseous air and condensate particles interact. We show that these assumptions cannot be simultaneously applicable to condensation and evaporation. "Reactive motion" leading to an upward acceleration of air during condensation does not exist. The "reactive motion" term can be justified for evaporation only; it describes the downward acceleration of air. We emphasize the difference between the equations of motion (i.e., equations constraining velocity) and those constraining momentum (i.e., equations of motion and continuity combined). We show that, owing to the imprecise nature of the continuity equations, consideration of total momentum can be misleading and that this led to the "reactive motion" controversy. Finally, we provide a revised and generally applicable equation for the motion of moist air.

physics.flu-dyn↗
arXiv2016

The water budget of a hurricane as dependent on its movement

Despite the dangers associated with tropical cyclones and their rainfall, the origins of storm moisture remains unclear. Existing studies have focused on the region 40-400 km from the cyclone center. It is known that the rainfall within this area cannot be explained by local processes alone but requires imported moisture. Nonetheless, the dynamics of this imported moisture appears unknown. Here, considering a region up to three thousand kilometers from storm center, we analyze precipitation, atmospheric moisture and movement velocities for North Atlantic hurricanes. Our findings indicate that even over such large areas a hurricane's rainfall cannot be accounted for by concurrent evaporation. We propose instead that a hurricane consumes pre-existing atmospheric water vapor as it moves. The propagation velocity of the cyclone, i.e. the difference between its movement velocity and the mean velocity of the surrounding air (steering flow), determines the water vapor budget. Water vapor available to the hurricane through its movement makes the hurricane self-sufficient at about 700 km from the hurricane center obviating the need to concentrate moisture from greater distances. Such hurricanes leave a dry wake, whereby rainfall is suppressed by up to 40 per cent compared to its long-term mean. The inner radius of this dry footprint approximately coincides with the radius of hurricane self-sufficiency with respect to water vapor. We discuss how Carnot efficiency considerations do not constrain the power of such open systems that deplete the pre-existing moisture. Our findings emphasize the incompletely understood role and importance of atmospheric moisture supplies, condensation and precipitation in hurricane dynamics.

physics.ao-ph↗
arXiv2013

Why does air passage over forest yield more rain? Examining the coupling between rainfall, pressure and atmospheric moisture content

The influence of forest loss on rainfall remains poorly understood. Addressing this challenge Spracklen et al. recently presented a pan-tropical study of rainfall and land-cover that showed that satellite-derived rainfall measures were positively correlated with the degree to which model-derived air trajectories had been exposed to forest cover. This result confirms the influence of vegetation on regional rainfall patterns suggested in previous studies. However, we find that the conclusion of Spracklen et al. -- that differences in rainfall reflect air moisture content resulting from evapotranspiration while the circulation pattern remains unchanged -- appears undermined by methodological inconsistencies. We identify methodological problems with the underlying analyses and the quantitative estimates for rainfall change predicted if forest cover is lost in the Amazon. We discuss some alternative explanations that include the distinct role of forest evapotranspiration in creating low pressure systems that draw moisture from the oceans to the continental hinterland. Our analysis of meteorological data from three regions in Brazil, including the central Amazon forest, reveal a tendency for rainy days during the wet season with column water vapor (CWV) exceeding 50 mm to have higher pressure than rainless days; while at lower CWV rainy days tend to have lower pressure than rainless days. The coupling between atmospheric moisture content and circulation dynamics underlines that the danger posed by forest loss is greater than suggested by focusing only on moisture recycling alone.

physics.ao-ph↗
arXiv2012

The key physical parameters governing frictional dissipation in a precipitating atmosphere

Precipitation generates small-scale turbulent air flows the energy of which ultimately dissipates to heat. The power of this process has previously been estimated to be around 2-4 W m-2 in the tropics: a value comparable in magnitude to the dynamic power of the global circulation. Here we suggest that this previous power estimate is approximately double the true figure. Our result reflects a revised evaluation of the mean precipitation path length Hp. We investigate the dependence of Hp on surface temperature,relative humidity,temperature lapse rate and degree of condensation in the ascending air. We find that the degree of condensation,defined as the relative change of the saturated water vapor mixing ratio in the region of condensation, is a major factor determining Hp. We estimate from theory that the mean large-scale rate of frictional dissipation associated with total precipitation in the tropics lies between 1 and 2 W m-2 and show that our estimate is supported by empirical evidence. We show that under terrestrial conditions frictional dissipation constitutes a minor fraction of the dynamic power of condensation-induced atmospheric circulation,which is estimated to be at least 2.5 times larger. However,because Hp increases with surface temperature Ts, the rate of frictional dissipation would exceed that of condensation-induced dynamics, and thus block major circulation, at Ts >~320 K in a moist adiabatic atmosphere.

physics.ao-ph↗
arXiv2010

Comprehending environmental and economic sustainability: Comparative analysis of stability principles in the biosphere and free market economy

Using the formalism of Lyapunov potential function it is shown that the stability principles for biomass in the ecosystem and for employment in economics are mathematically similar. The ecosystem is found to have a stable and an unstable stationary state with high (forest) and low (grasslands) biomass, respectively. In economics, there is a stable stationary state with high employment, which corresponds to mass production of conventional goods sold at low cost price, and an unstable stationary state with lower employment, which corresponds to production of novel goods appearing in the course of technological progress. An additional stable stationary state is described for economics, the one corresponding to very low employment in production of life essentials such as energy and raw materials. In this state the civilization currently pays 10% of global GDP for energy produced by a negligible minority of the working population (currently ~0.2%) and sold at prices greatly exceeding the cost price by 40 times. It is shown that economic ownership over energy sources is equivalent to equating measurable variables of different dimensions (stores and fluxes), which leads to effective violation of the laws of energy and matter conservation.

q-fin.GN↗
arXiv2010

Reply to comment of Bister and co-authors on the critique of the dissipative heat engine

The dissipative heat engine (DHE) is based on a Carnot cycle with external heat Qin received at temperature Ts and released at To < Ts. In contrast to the classical Carnot engine, mechanical work Ad in the DHE is not exported to external environment but dissipates to heat within the engine. Makarieva et al. (2010, hereafter MGLN) asserted that the laws of thermodynamics prohibit an increase of Ad beyond the Carnot limit: Ad <= epsilon Qin, epsilon = (Ts - To)/Ts. Bister et al. (2010, hereafter BRPE) counterargued that such an increase is possible and that hurricanes can be viewed as a natural DHE. Here we show that the arguments of BRPE are not consistent with the energy conservation law and thus do not refute MGLN's claims.

physics.ao-ph↗
arXiv2007

Resonance and frequency-locking phenomena in spatially extended phytoplankton-zooplankton system with additive noise and periodic forces

In this paper, we present a spatial version of phytoplankton-zooplankton model that includes some important factors such as external periodic forces, noise, and diffusion processes. The spatially extended phytoplankton-zooplankton system is from the original study by Scheffer [M Scheffer, Fish and nutrients interplay determines algal biomass: a minimal model, Oikos \textbf{62} (1991) 271-282]. Our results show that the spatially extended system exhibit a resonant patterns and frequency-locking phenomena. The system also shows that the noise and the external periodic forces play a constructive role in the Scheffer's model: first, the noise can enhance the oscillation of phytoplankton species' density and format a large clusters in the space when the noise intensity is within certain interval. Second, the external periodic forces can induce 4:1 and 1:1 frequency-locking and spatially homogeneous oscillation phenomena to appear. Finally, the resonant patterns are observed in the system when the spatial noises and external periodic forces are both turned on. Moreover, we found that the 4:1 frequency-locking transform into 1:1 frequency-locking when the noise intensity increased. In addition to elucidating our results outside the domain of Turing instability, we provide further analysis of Turing linear stability with the help of the numerical calculation by using the Maple software. Significantly, oscillations are enhanced in the system when the noise term presents. These results indicate that the oceanic plankton bloom may partly due to interplay between the stochastic factors and external forces instead of deterministic factors. These results also may help us to understand the effects arising from undeniable subject to random fluctuations in oceanic plankton bloom.

q-bio.PE↗
arXiv2007

Emergence of spatiotemporal chaos driven by far-field breakup of spiral waves in the plankton ecological systems

Alexander B. Medvinsky \emph{et al} [A. B. Medvinsky, I. A. Tikhonova, R. R. Aliev, B.-L. Li, Z.-S. Lin, and H. Malchow, Phys. Rev. E \textbf{64}, 021915 (2001)] and Marcus R. Garvie \emph{et al} [M. R. Garvie and C. Trenchea, SIAM J. Control. Optim. \textbf{46}, 775-791 (2007)] shown that the minimal spatially extended reaction-diffusion model of phytoplankton-zooplankton can exhibit both regular, chaotic behavior, and spatiotemporal patterns in a patchy environment. Based on that, the spatial plankton model is furtherly investigated by means of computer simulations and theoretical analysis in the present paper when its parameters would be expected in the case of mixed Turing-Hopf bifurcation region. Our results show that the spiral waves exist in that region and the spatiotemporal chaos emerge, which arise from the far-field breakup of the spiral waves over large ranges of diffusion coefficients of phytoplankton and zooplankton. Moreover, the spatiotemporal chaos arising from the far-field breakup of spiral waves does not gradually involve the whole space within that region. Our results are confirmed by means of computation spectra and nonlinear bifurcation of wave trains. Finally, we give some explanations about the spatially structured patterns from the community level.

nlin.PS↗
arXiv2006

Spreading of infectious diseases on complex networks with non-symmetric transmission probabilities

We model the spread of a SIS infection on Small World and random networks using weighted graphs. The entry $w_{ij}$ in the weight matrix W holds information about the transmission probability along the edge joining node $v_i$ and node $v_j$. We use the analogy between the spread of a disease on a network and a random walk performed on this network to derive a master equation describing the dynamics of the process. We find conditions under which an epidemic does not break out and investigate numerically the effect of a non-symmetric weight distribution of the initially infected individual on the dynamics of the disease spread.

math.GM↗